Waferboards are sometimes used as a sub-floor and overlayed with some form of decorative cover such as carpet, hardwood, etc. One of the major problems in using panels such as wood particle board (waferboard) is that on significant wetting the boards tend to expand non-uniformly i.e. the edges of the board tend to swell more than the central portion and produce a ridge having a relatively clear line of demarkation between the swelled edge (ridge) and the remainder of the panel. It is believed this edge swell is caused primarily because the edges of the board absorb more water. Furthermore the side edges are normally tongue and grooved so that swelling prior to assembly of the boards to form the sub-floor can result in difficulties and possibly even damage to the boards when fitting the tongues and grooves.
Techniques have been devised to stabilize wafer board product and to reduce springback after wetting. One such process is described in U.S. Pat. No. 32,173,460 issued Mar. 16, 1965 to Hann wherein the whole board is contained within fixed boundaries, i.e. prevented from significant expansion and exposed to steam thereby causing internal swelling and promotion of plastic flow which in effect stabilized the product.
Canadian Pat. Nos. 1,213,707 and 1,215,510 issued Nov. 12, 1986 and Dec. 23, 1986 respectively to Hsu disclosed other treatments for improving the dimensionally stability of a composite board. The earlier of the two patents discloses a secondary heat treatment wherein the finished board is subjected to an increased temperature for a pre-determined period of time while the latter patent discloses a system of presteaming the chips prior to forming the layup and making the board so that the moisture content of the chip is significantly higher and the chips are more plastic when they are being formed into a panel.
Steam pressing has also been found to improve the dimensional stability of a panel, i.e. when the panel is consolidated under pressure and at the same time steam is applied the resultant product tends to have greater dimensional stability than when a similar panel is produced without the addition of steam.